There is increasing evidence of disturbances of neurobiological processes in depression. Among numerous purported abnormalities, alterations of electroencephalographic (EEG) sleep profiles have been widely documented and replicated. It has been suggested that these disturbances may be state-dependent markers of clinical forms of endogenous depression (ED) which may not respond to psychotherapy. An adequate test of these speculations requires delivery of a form of psychotherapy, with proven efficacy in depressed patients, to a group of endogenous depressives evaluated with EEG sleep studies both before and after treatment. Existing research on EEG sleep profiles have dealt with patients who have received somatic therapies and, therefore, may have obscured the neurobiological changes associated with recovery with the direct effects of medication on central nervous system mechanisms. The current revised proposal addresses these issues directly. A sample of 50 out-patients with an RDC diagnosis of probable or definite ED will receive up to 12 weeks of treatment with Cognitive Behavior Therapy (CBT). Sleep studies will be completed at baseline and repeated after patients either have achieved a stable level of clinical remission or have completed the 12-week treatment protocol. Clinical evaluations conducted before, during and after acute treatment will include assessments of depressive symptomatology, cognitive variables, personality disorder, and life events. Planned statistical analyses will examine changes in EEG sleep variables as a function of time and clinical response. The efficacy of CBT will be compared in patients with and without shortened REM latency (2-night mean less than or equal to 60 minutes), a proposed indicator of nonresponse to psychosocial treatment. Potential interrelationships of change among affective, cognitive, psychosocial, and EEG sleep measures following treatment with CBT also will be explored. Results will increase understanding of the theoretical implications and practical applications of selected EEG sleep disturbances and will advance knowledge concerning the impact and efficacy of CBT of depression. Findings also may lead to improve methods of selection of specific types of treatment for depressed individuals. This is a revision of application 1 R01 MH 41884 01.